Hollow structures, or pressure vessels, here referred to as ‘vessels’ such as those used to store fluids and gases, particularly under pressure, such as pressurized gas tanks are generally made from metals such as steel or aluminium, or from composite materials.
Storage of certain media requires a barrier liner within the vessel to prevent loss or vessel structural damage. For example gases in composite tanks (permeability levels of pure composite too high leading to gas loss) or hydrogen in steel vessels (possibility of embrittlement). The storage of other liquids, such as water, often requires a barrier liner to avoid adverse effects on the structural components.
Barrier liners exist for certain vessel forms, e.g. HDPE liners in filament-wound composite vessels for gas storage, and metalized layers have found use in both composite and metal tanks to improve resistance to permeability of media and damage to structural integrity. An example would be the aluminium liners used in composite vessels designed for the storage of natural gas for vehicular applications.
Certain polymer based liners offer good resistance to permeability, heat and chemical attack making them suitable for high pressure media storage.
High pressure vessels require pressure monitoring for safety fill quantity, leakage etc. This is usually achieved through pressure sensors and regulators at the vessel neck. Drawbacks of existing technology for pressure sensing in vessels comprise the necessary requirements for additional parts to be fixed postproduction, involving extra costs and fabrication steps. In addition, most pressure gauges are fitted to the tank only during service, so during storage and/or transportation phases, the pressure level in the tank is often unknown.
An externally mounted pressure gauge is unlikely to have the sensitivity to detect minute leaks in a vessel due to the initiation of sub-critical flaws in the tank or liner structure unless it has been specifically designed to do so, which is costly.